Both clinical and radiographic heterogeneity has been described in the Alzheimer's disease (AD) patient population. This may relate to the variety of both genetic and environmental etiologies which underlie this clinical presentation. We suggest that recent work in etiology of Parkinson's disease (PD) may serve as a model for future investigations in AD. It is our hypothesis that exposure to herbicides and pesticides increase the risk of developing AD. We propose to conduct a case-control study to determine the risk of farming and rural lifestyle in AD. We will study the herbicide/pesticide exposure of patients with AD, as compared to age and gender matched controls. We will determine if there are differences in risk regarding herbicide/pesticide exposure, farming vs. non-farming occupations, living in a rural environment or drinking well water vs. city water. We will determine the familial risk in families of AD patients of developing PD, developing AD, and the interaction between environmental and genetic risks in our AD patient population. Relatives, including spouse and siblings, of all patients who present to the clinical core and meet entry criteria will be evaluated. They will undergo an interview regarding places of residence, occupations, and exposure to herbicides/pesticides. At least two family members will be interviewed regarding history of AD, PD, and other related conditions in the subject's first degree relatives. Individuals with herbicide/pesticide exposure via occupation or environment will be questioned with regard to quantification and details of exposure. Statistical measures will be used to determine if significant differences exist in AD with regard to rural living, farming, water supply, and herbicide/pesticide exposure. Age-specific morbid risk in first degree relatives will be determined for AD, PD, and other potentially associated conditions. Multiple logistic regression will be used to examine whether genetic, environmental, or synergistic combinations are more predictive of morbid risk of developing AD.